In the drilling of an oil or gas well, a sample of the formation which has been tapped is often analyzed to determine the quality of the formation. The information obtained includes the amount of oil and gas, carbon dioxide, and water contained in the formation. This information is used in various ways, such as deciding whether the formation will be produced, or whether the well will be capped and abandoned.
Prior art methods of analyzing the content of the subterranean formation have involved drilling a well core in the formation with a well coring device. The well core is retrieved and analyzed.
However, in such prior art methods, significant information concerning the subterranean formation is often lost due to the pressure differential between the subterranean formation and the surface of the earth where the analysis is conducted. Subterranean formations generally contain fluid and gas under enormous pressure. During the taking of the core sample, this pressure is opposed by a column of mud. When the core is retrieved from the well, the pressure is released, causing the fluids contained in the formation to flow or "bleed" from the core. Thus, prior art cores have often lost a significant fraction of the fluids contained in the core. Accurate analysis without an accounting for the lost fluid is difficult.
A prior method of accounting for the lost fluid has been to maintain the core under pressure after it has been drilled and then freezing the core until analysis in a lab.
A need has thus arisen for a convenient and inexpensive method and apparatus for accurately determining information regarding fluid in subterranean formations.